Tissue buckling as a mechanism of bioprosthetic valve failure

Current reports indicate that collagen fiber disruption resulting from cyclic leaflet bending is a factor determining long-term durability of bioprosthetic heart valves. Examination of the opening characteristics of porcine xenografts has shown two areas of high bending curvature that correlate well with sites of leaflet tearing. These are at the free edge and near the attachment of the leaflets to the aortic root. To determine the potential effects of sharp bends in leaflet material, we examined 15 strips each of fresh and glutaraldehyde-treated porcine aortic valve tissue. Leaflet strips were bent to curvatures of 0.18 mm-1 to 6.67 mm-1, histologically processed, sectioned, and examined under a light microscope. We observed severe compressive buckling in the samples taken from bioprosthetic valves but little in the fresh-tissue samples. At physiological curvatures (less than 0.28 mm-1), no buckling occurred in the fresh tissue; at high bending curvatures (2.0 mm-1), the depth of buckling observed in the treated tissue was 100% greater than that in the fresh. We believe that porcine xenograft failure is related to compressive buckling of the aldehyde-treated tissue and is mediated by the systematic breaking of collagen fibers at the site of buckling. We suggest that alternative valve designs and preservation techniques be employed to prevent such abnormal leaflet deformations.